When using a luminous element of finite size, for instance a filament of an electric bulb, e.g. a halogen cycle incandescent lamp, in combination with a smooth reflector surface, local brightness variations occur in the film of a projector window due to the filament image. For this reason, it has been proposed to roughen the reflector surface by punching or facetting. A reflector having a surface of numerous small reflective areas is described for instance in U.S. Pat. No. 4,021,659 and U.S. Pat. No. 4,035,631. Other surface structures are described, among others, in German Disclosure Documents DE-OS No. 21 48 478 and DE-OS No. 23 63 378 to which U.S. Pat. Nos. 3,758,770, Morasz and 3,825,742, Levin correspond. The structures of the reflector surfaces described cause the beams to become fanned out or spread more than with a smooth reflector surface. Thus, the filament structure in the film window is blurred; non-uniformities in the film window illumination remain nevertheless. As a result of increased stray light, the utilizable light flux drops, and this has to be compensated by increasing the power input of the lamp; this, in turn, causes a higher temperature in the film window than with smooth reflector surfaces. The common feature of all these solutions is that the reflectors have one contour only.